1. Field of the Invention
The present invention relates to an Internet telephone connection method for performing a call connection, etc. to a PSTN (public switched telephone network) through a gateway device for use in an Internet telephone system having a gateway device, a gate keeper, a bandwidth controller, and a router, etc.
2. Description of the Related Art
A method of implementing a protocol for servicing a telephone call from Internet to a PSTN is provided in Recommendation H.323 of ITU-T (International Telecommunication Union-Telecommunication Standardization Sector). In H.323, a gateway device for performing the interconnection processing between a PSTN and the Internet, and a gate keeper for managing/controlling plural gateway devices are used as main constituent elements. The gateway device performs conversion of a call control protocol and audio signals between the PSTN and the Internet. The gate keeper serves to manage the gateway devices in a zone under its control, and mainly performs selection of a connection destination gateway, authorization and admission control of a calling side, and allocation of a telephonic communication bandwidth in response to a call setup request from an IP (Internet Protocol) terminal or a gateway device.
In a case where a gateway device at a calling side (i.e., a call source), a gateway device at a called side (call destination) and a gate keeper are provided, the calling side gateway device which accepts a call reception from a PSTN assigns a connection condition such as the telephone number of a connection destination, etc. and inquires to the gate keeper. In response to this inquiry, the gate keeper determines the address of a called side gateway device which satisfies the request condition, and notifies it to the calling side gateway device. Subsequently, the calling side gateway device proceeds in the connection of the call to the called side gateway device. When a call setup is accepted between the gateway devices at the calling side and the called side, audio data are transmitted/received according to a protocol for transferring real-time data. In other words, the three-step procedures, that is, a procedure of determining the gateway device of a connection destination, a procedure of connecting a call to the gateway device thus determined and a procedure of transferring real-time information between the gateway devices thus connected are carried out for the call connection. The calling side gateway device may be designed in the form of an IP terminal having a telephone function.
Guidelines for the attribute information of the gateway device is specified in “a Framework for a Gateway Location Protocol” (IPTEL Working Group, Jul. 7, 1998) which has been considered by IETF (Internet Engineering Task Force). According to the guidelines, an assembly of gateway devices managed by the same gate keeper are defined as a zone, and it is assumed to extend to a form comprising plural zones. As the attribute information of the gateway device, there is provided the phone prefixes allowed, the address of a gateway device, the specification for voice coding, a signal protocol to be supported, a cost plan, a billing method, the confederation of membership, a total line capacity, an available line capacity, information concerning additive features supported, etc.
Here, the phone prefixes allowed represents an assembly of connectable telephone numbers when a connection is made from the gateway device thereof to a PSTN. Such attribute information is generally set in each gateway device by a maintainer or the like. In the following description, information causing a problem in connection such as a signal protocol supported by the phone prefixes allowed in the attribute information is referred to as “end-end attribute information”.
The standardization of IETF aims to specify means for automatically registering the above attribute information into a gate keeper and means for informing the information to other gate keepers. With these means, when a new gateway device is connected to the Internet, the attribute information to be informed is automatically distributed to all the gate keepers which are mutually connected to one another using the protocol.
According to the model provided in IETF, there are assumed not only a case where only one gateway device is selected by the gate keeper, but also a case where a destination gateway device is selected from plural choices. Accordingly, if a gateway device at a calling side is aware of any problem/congestion condition or the like at a called side, a backup mechanism to enhance the reliability could be implemented. An available line capacity and an operation/stop state of the gateway device itself may be considered as the attribute information on the problem/congestion condition.
After a gateway device at a connection destination is selected and a pair of gateway devices are determined, a call connection is carried out according to the procedure of H.323. Whether a desired bandwidth can be secured between the gateway devices becomes clear after the protocol procedure after the connection proceeds. Therefore, if the Internet is in a congested condition, a desired quality of connection may not be provided. There is proposed a gateway device having a communication bandwidth reserving procedure such as RSVP (Resource Reservation Protocol) standardized in IETF, as described in Chapter 2 of “Delivering Voice over IP Networks” (written by D. Minoli, E. Minoli). The RSVP procedure is a procedure for reserving a one-way bandwidth from a called side to a calling side. According to this procedure, bandwidths are successively ensured via routers from the application at the called side to the application at the called side. In this case, reservations requesting the same bandwidth from both the sides are needed for voice traffic which needs a symmetrical bandwidth between upward and downward directions. If each application reserves a desired bandwidth with no limitation, a bandwidth-over event would occur and it is generally known that it is impossible to implement the perfect bandwidth guarantee in RSVP.